The invention concerns a method and a system for configuring a beam forming antenna in a communication network transporting data.
In communication networks using high transmission frequencies, for example around 60 GHz, the signals require direct transmission, that is to say without reflection, from the source or transmitter. Such a direct transmission is also called Line of Sight (LOS).
Wireless personal area networks (W-PANs) use this kind of frequency. These networks are particularly well suited to A/V (Audio/Vidéo) applications requiring ever higher data bit rates on the order of a few Gigabits per second as well as an increasingly higher quality of services.
However, the power of the directly transmitted signals is attenuated rapidly as they are propagated.
So that the receiver has a sufficient signal to noise ratio, several methods are possible.
Thus recourse may be had to antenna techniques such as combining multiple receiving or transmitting antennas.
It is also possible to use techniques of cooperation between nodes in a network for relaying the signals transmitted.
In a communication network comprising one or more nodes serving as relays and which uses high transmission frequencies, the transmitting antenna must have high gain.
This is because high gain is necessary for being able to transmit a signal to a distant receiver (for example a receiver placed at 10 meters in a radio network where the carrier is 60 GHz) while complying with the constraints on the transmission power, which must remain compatible with the safety of persons.
Since the gain of an antenna is all the greater, the more the antenna is directive (that is to say the narrower the beam), it is necessary to perform a precise aiming of the antenna.
However, such a setting of the antenna requires the knowledge of the direction of arrival of the signal.
In a small network (the distance between the transmitter and the receiver is for example less than 10 meters), a small movement of the transmitter or receiver in a direction that does not correspond to the one to which the lobe or lobes of the antenna extend is liable to cause defective aiming.
In addition, as the useful rate required for transporting data over the network is very high, it is not appropriate to devote time to aiming.
Moreover, forming an antenna lobe at the transmitter from a return of information from a receiver is known from the prior art.
Thus, for example, the U.S. Pat. No. 7,151,951 is known, which discloses a method making provision for using information coming from the nodes of a network for calculating coefficients acting on the amplitude and phase of the signals applied to the elements of an antenna. These coefficients will make it possible to adjust a transmitting antenna capable of generating multiple beams in the context of the 3GPP network.
According to this method, each node in the network transmits a return channel that carries either antenna setting coefficients or information for calculating these coefficients.
However, this method is not entirely satisfactory.
This is because it is not particularly suited to the topology of the network.
Moreover, this method makes it possible to broadcast a message in the network in CDMA mode after having encoded it.
Thus, each receiving node receives a physical signal, each being different from one receiver to another since each signal is orthogonal to the other signals.
This method is therefore not applicable to the reception of the same physical signal at all the receivers.
Furthermore, such a method involves operations at the transmitting node which are costly in terms of resources.
In particular, the orthogonal signals have to be elaborated and encoded using relatively long codes before being transmitted.
Also, the transmission of these signals requires relatively high bandwidth resources.
Another method is known from WO 2006/088400.
According to this method a signal is divided at a transmitting node into substreams which are each transmitted to a different relay node.
The relay nodes provide feedback channel state information to the transmitting node so that the latter adjusts its antenna weighting matrix.
This latter method suffers from the same drawbacks as the former method briefly described above.